Mutations in ion channel proteins associated with sudden cardiac death

ABSTRACT

Previously unknown mutations of the KCNH2, SCN5A and KCNQ1 genes are disclosed which are involved in ion channel disruptions associated with short QT syndrome, long QT syndrome, Brugada syndrome and progressive conduction disease. These mutations are utilized to diagnose and screen for short QT syndrome, long QT syndrome, Brugada syndrome and progressive conduction disease, thus providing modalities for diagnosing sudden cardiac death and/or predicting susceptibility to sudden cardiac death. Nucleic acid probes are provided which selectively hybridize to the mutant nucleic acids described herein. Antibodies are provided which selectively bind to the mutant proteins described herein. The mutations described herein are also utilized to screen for compounds useful in treating the symptoms manifest by such mutations.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from U.S. Provisional Application No. 60/497,256, filed Aug. 22, 2003, the entire contents of which are hereby incorporated by reference.

BACKGROUND

1. Technical Field

The invention relates to diagnosis of sudden cardiac death or potential for sudden cardiac death in patients who have mutations in ion channels proteins involved in electrophysiology of the heart.

2. Background of Related Art

Sudden cardiac death takes the lives of over 300,000 Americans annually. Malignant ventricular arrhythmias occurring in individuals with structurally normal hearts account for a subgroup of these sudden deaths. This form of cardiac disease accounts for approximately 20% of sudden cardiac death cases. Recent years have witnessed major strides in the understanding of sudden cardiac death in individuals with structurally normal heart. Idiopathic, sudden cardiac death syndromes for which there was previously no explanation are gradually coming into focus as forms of inherited ion channelopathies.

The QT interval is the surrogate electrocardiographic index of ventricular repolarization and its duration under normal conditions is mainly determined by expression, properties, and balance of the repolarising inward sodium and calcium and outward potassium and chloride currents. Ion channels proteins are responsible for the currents that comprise the cardiac action potential and alterations in ion channel function are known to be associated with a wide spectrum of phenotypes. Long QT syndrome (LQT) is characterized by the appearance of a long QT interval in the electrocardiogram, and an atypical polymorphic ventricular tachycardia known as torsades de pointes, and a high risk of sudden cardiac death. Congenital LQT syndrome is an inherited condition of abnormal cardiac repolarization. Acquired LQT syndrome is similar to congential LQT syndrome but can be caused by exposure to drugs, trauma or other environmental factors. Gain of function in SCN5A, the gene that encodes for the α subunit of the cardiac sodium channel, is associated with the LQT3 form of the Long QT syndrome (See, e.g., U.S. Pat. No. 5,599,673), while a decrease in function of the same channel is associated with Brugada syndrome and familial conduction disease. Likewise, loss of function in I_(Ks) and I_(Kr) is linked to other forms of Long QT, while an increase in I_(Ks) current, caused by a mutation in the α subunit KCNQ1 (also referred to as KvLQT1), is linked to familial atrial fibrillation. The final common pathway is similar, involving alteration of ion channel activity, leading to the development of an arrhythmogenic substrate.

U.S. Pat. Nos. 6,582,913, 6,451,534, 6,432,644 and 6,277,978 are directed to screening and/or diagnosis of Long QT syndrome by analyzing the DNA sequence of the KvLQT1 or KCNE1 genes and molecular variants of these genes which cause or are involved in the pathogenesis of Long QT syndrome. U.S. Pat. Nos. 6,420,124 and 6,274,332 are directed to screening for drugs useful in treating a person having certain mutations in the KvLQT1 or KCNE1 genes. U.S. Pat. No. 6,458,542 is directed to a method for screening for susceptibility to drug induced cardiac arrhythmia by detecting a polymorphism in the KCNE1 gene. Certain mutations in the HERG (also known as KCNH2) gene have also been linked to LQT synndrome. See, e.g., U.S. Pat. No. 6,207,383.

Brugada syndrome is associated with sudden cardiac death and ventricular arrhythmia and may occur in the structurally normal heart. It is characterized by ST segment elevation in the right precordial leads (V1 to V3) and right bundle branch block. The age of onset of clinical manifestations, which can include syncope or cardiac arrest, is typically in the third or fourth decade of life. Cardiac events may occur during sleep or at rest. A loss of ion channel function in Brugada syndrome has been associated with certain mutations of the SCN5A protein.

Progressive cardiac conduction defect, also known as progressive conduction disease or Lenegre disease is another electrophysiological cardiac syndrome that is considered one of the most common. It is characterized by a progressive alteration of cardiac conduction through the atrioventricular node, His-Purkinje system with left or right bundle block, which may cause syncope or sudden death. Scott et al., Nat. Genet., (1998) 23:20-21, indicate that certain mutations in SCN5A are associated with progressive conduction disease.

Short QT syndrome (SQT) is a new clinical entity originally described in 2000. Short QT syndrome is characterized by the presence of a very short QT interval in the electrocardiogram (Bazzett-corrected QT interval (QTc) of ≦300 msec), episodes of paroxysmal atrial fibrillation, ventricular arrhythmias and possible sudden death in patients with structurally normal hearts. An autosomal dominant pattern of transmission with a high incidence of sudden death over several generations has been reported.

There is a need to determine the underlying cause of sudden cardiac death so that diagnostic procedures can be implemented to take precautions in susceptible individuals and to aid in determinations of mortality risk.

SUMMARY

In one aspect, the genetic basis for a new clinical entity, characterized by sudden death and short QT intervals in the electrocardiogram is identified. Two different missense mutations are associated with the same amino acid change (N588K) in the S5-P loop region of the cardiac I_(Kr) channel HERG (KCNH2). The mutations dramatically increase I_(Kr) leading to heterogeneous abbreviation of action potential duration and refractoriness.

In another aspect, previously unknown mutations in the SCN5A gene are associated with Brugada syndrome. Mutations at the following positions in the protein encoded by SCN5A (also known as Na_(v)1.5) are identified herein as R104W, R179 stop, T220I, G400A, E446K, F532C, A735V, R878C, H886P, L917R, E1573K, C1727R, V232I+L1307F, P336L+I1659V, Y1614 stop, deletion from E1573-G1604, and insertion of TG at 851.

In another aspect, a previously unknown mutation in the KCNQ1 protein is associated with Long QT syndrome, namely, G189W. In another aspect, previously unknown mutations of the protein encoded by the KCNH2 gene, namely, R356H, a C deletion at 764, and a W398 stop are associated with Long QT syndrome. In another aspect, a previously unknown mutation of the protein encoded by SCN5A (Na_(v)1.5), namely, S1134I, is associated with Long QT syndrome.

In another aspect, a previously unknown mutation of the protein encoded by SCN5A (Na_(v)1.5), namely, P1008S, is associated with progressive conduction disease.

In accordance with the present invention, the above-identified mutations are utilized to diagnose and screen for sudden cardiac death or to determine susceptibility to cardiac death. Nucleic acid probes are provided which selectively hybridize to the mutant nucleic acids described herein. Antibodies are provided which selectively bind to the mutant proteins described herein. The above-identified mutations are also utilized to screen for drugs useful in treating the symptoms manifest by such mutations.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the pedigree of families 30-371 and 30-335 with familial Short QT syndrome. Filled circles and squares indicate affected individuals with abnormal QT interval. Half-filled circles and squares indicate individuals who suffered sudden cardiac death. Crossed circles and squares indicate deceased individuals.

FIG. 2 illustrates DNA sequencing analysis of with a C to A (family 30-371) and a C to G (family 30-335) substitution in exon 7 of KCNH2. This results in the same amino acid substitution of lysine for asparagine at codon 588 (N588K).

FIG. 3 illustrates mutation N588K removed inactivation of KCNH2. A) Series of wild type KCNH2/KCNE2 currents elicited by 800 ms depolarizing pulses in increments of 10 mV between −50 and 50 mV from a holding potential of −80 mV. A large tail inward current is observed upon repolarization to −100 mV. B) Same protocol as in A applied on TSA201 cells transfected with the mutant channel N588K. Developing currents are dramatically increased due to loss of rectification properties of the channel and the tail currents were abolished by the mutation. C) Normalized current voltage relationship. Current amplitude was normalized to the value at 0 mV (maximum for WT). D) Currents recorded during an action potential clamp. Dotted line: WT, solid line: N588K. N588K thus leads to a dramatic gain of function in IKr.

FIG. 4 illustrates an electrocardiogram of patient IV-5 before and after the administration of Sotalol 1 mg/kg body weight intravenously. Electrocardiogram shows leads I to III at 25 mm/s. QTc changes minimally from 291 to 302 msec.

FIG. 5 illustrates the effect of sotalol on KCNH2 currents in human embryonic kidney cells (TSA201) transformed with WT KCNH2/KCNE2 compared with TSA201 cells transformed with N588K KCNH2/KCNE2 using patch clamp experiments. Recordings of WT and N588K currents during a 800-ms pulse to +20 mV (Vh=−80 mV) repeated every 15 seconds in control and 10 min after addition of 100 and 500 μM D-sotalol. Concentration-response relation is represented graphically for WT and N588K currents are expressed as percent of control values following application of D-sotalol. Data: Mean±SEM (n=4-6 cells for each point). IC₅₀ is shifted from 0.137 mM in WT to 2.82 mM in the N588K mutant. The N588K mutation reduced sensitivity to sotalol by 20-fold.

FIG. 6 illustrates the effect of quinidine on KCNH2 currents in human embryonic kidney cells (TSA201) transformed with WT KCNH2/KCNE2 compared with TSA201 cells transformed with N588K KCNH2/KCNE2 using patch clamp experiments. Recordings of WT and N588K currents during a 800-ms pulse to +20 mV (Vh=−80 mV) repeated every 15 seconds in control and 10 min after addition of 5 μM quinidine. Dose-response relation is represented graphically for WT and N588K currents are expressed as percent of control values following application of quinidine. Data: Mean±SEM (n=4-6 cells for each point). IC₅₀ is shifted from 0.75 mM in WT to 4.35 mM in the N588K mutant. The N588K mutation reduced sensitivity to quinidine by 5.8 fold.

FIG. 7 illustrates representative whole cell current recordings for WT (Panel A) and SCN5A F532C Brugada syndrome mutant (Panel B) in transfected TSA201 cells. Current recordings were obtained at test potentials between −100 and 0 mV in 5 mV increments from a holding potential of −120 mV. Panel C: Normalized I-V relation for WT (n=9) and F532C (n=9) channels. Panel D: Steady state-activation relation for WT and F532C. Chord conductance was determined using the ratio of current to the electromotive potential for the 9 cells shown in Panel C. Data were normalized and plotted against their test potential.

FIG. 8 illustrates representative steady-state inactivation recordings for wild-type (WT) (Panel A) and SCN5A F532C (Panel B) observed in response to the voltage clamp protocol (top of figure). Panel C: Peak current was normalized to their respective maximum values and plotted against the conditioning potential. The steady state inactivation relation measured with the F532C mutation shows a −10 mV shift of mid-inactivation voltage in the hyperpolarizing direction (−102.4±4.8; n=9 versus −92.3±2.4 for WT; n=10; P<0.05).

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In accordance with the present invention, previously unknown mutations of genes and their corresponding proteins are disclosed which are involved with ion channels associated with arrhythmias and/or sudden cardiac death.

In one aspect, the invention relates to the identification of a molecular basis of short QT syndrome. More specifically, a missense mutation in the KCNH2 gene (Seq. Id. No. 6) (also referred to as the HERG gene) causes a N588K mutation of the KCNH2 protein (Seq. Id. No. 5) and short QT syndrome. Although arrhythmic diseases have been linked to gain of function, e.g., in SCN5A (late I_(Na)) and KCNQ1 (I_(Ks)), no disease had previously been associated with a gain of function in KCNH2 encoding for I_(Kr). The N588K mutation dramatically increases I_(Kr) leading to heterogeneous abbreviation of action potential duration and refractoriness, and a reduction of the affinity of the channel to I_(Kr) blockers. A novel genetic and biophysical mechanism is described herein which may be responsible for Sudden Infant Death Syndrome (SIDS), sudden death in children and in young adults caused by mutations in KCNH2. KCNH2 is the binding target for several cardiac and non-cardiac pharmacologic compounds.

In another aspect, previously unknown mutations in the SCN5A gene (Seq. Id. No. 4) are associated with Brugada syndrome. Mutations at one or more of the following positions in the protein encoded by the SCN5A gene (Na_(v)1.5) (Seq. Id. No. 3) are identified herein as R104W, R179 stop, T220I, G400A, E446K, F532C, A735V, R878C, H886P, L917R, E1573K, C1727R, V232I+L1307F, P336L+I1659V, Y1614 stop codon, deletion from E1573-G1604, and insertion of TG at 851.

In another aspect, a previously unknown mutation in the KCNQ1 protein (Seq. Id. No. 1), G189W is associated with Long QT syndrome. In another aspect, previously unknown mutations of the protein encoded by KCNH2 nucleic acid, namely, at least one of R356H, a C deletion at 764, and a W398 stop, are associated with Long QT syndrome. In another aspect, a previously unknown mutation of the protein encoded by SCN5A (Na_(v)1.5), namely, S1134I, is associated with Long QT syndrome.

In another aspect, a previously unknown mutation of the protein encoded by SCN5A (Na_(v)1.5), namely, P1008S, is associated with progressive conduction disease.

Analysis of these genes provides an early diagnosis of subjects with short QT syndrome (mutated KCNH2 as described above), Brugada syndrome (mutated SCN5A as described above), Long QT syndrome (mutated KCNQ1, KCNH2 and/or SCN5A as described above), and progressive conduction disease (mutated SCN5A as described above). Diagnostic methods include analyzing the nucleic acid sequence of any or all the KCNH2 (Seq. Id. No. 6), SCN5A (Seq. Id. No. 4), KCNQ1 (Seq. Id. No. 2) genes of an individual to be tested and comparing them with the nucleic acid sequence of the native, nonvariant gene. Alternatively, the amino acid sequence of the respective polypeptides encoded by the aforelisted genes may be analyzed for the above-indicated mutations which respectively cause short QT syndrome, Brugada syndrome and/or progressive conduction disease. Pre-symptomatic diagnosis of these syndromes will enable practitioners to treat these disorders using existing medical therapy, e.g., using I_(Kr) blocking agents, beta blocking agents or through electrical stimulation.

The present invention provides methods of screening the KCNH2, KCNQ1, and/or SCN5A genes to identify the mutations listed above. Such methods may include the step of amplifying the respective portions of the KCNH2, KCNQ1, and/or SCN5A genes containing and flanking the above described mutated sites, and may further include a step of providing a set of polynucleotides which are primers for amplification of said respective portions of the KCNH2, KCNQ1, and/or SCN5A genes. Methods of making such primers are well within the ordinary skill in the art. The methods are useful for identifying mutations for use in either diagnosis of short QT syndrome (mutated KCNH2 as described above), Brugada syndrome (mutated SCN5A as described above), Long QT syndrome (mutated KCNQ1, KCNH2 and/or SCN5A as described above), and progressive conduction disease (mutated SCN5A as described above) or prognosis of short QT syndrome (mutated KCNH2 as described above), Brugada syndrome (mutated SCN5A as described above), Long QT syndrome (mutated KCNQ1, KCNH2 and/or SCN5A as described above), and progressive conduction disease (mutated SCN5A as described above). The present invention is further directed to methods of screening humans for the presence of KCNH2 gene variants which cause short QT syndrome, the SCN5A variants which cause Brugada syndrome, the KCNQ1, KCNH2 and/or SCN5A variants which cause LQT syndrome, and/or the SCN5A variants which cause progressive conduction disease. Assays can be performed to screen persons for the presence of the above-described mutations in either the nucleic acid encoding the polypeptide, the polypeptide itself and/or fragments thereof. In one embodiment, the assay may be a microchip or microarray assay. The nucleic acid encoding the polypeptide and/or the polypeptide itself or a fragment thereof may also be used in assays to screen for drugs which will be useful in treating or preventing the occurrence of short QT syndrome.

The present invention also provides nucleic acid probes which will respectively and selectively hybridize to nucleic acid coding for KCNH2, KCNQ1 or SCN5A polypeptides containing the above-described mutations, for example, the mutation which causes short QT syndrome, said mutation being a substitution of lysine for asparagine at amino acid residue 588 of the KCNH2 polypeptide, but will not hybridize to DNA encoding wild type KCNH2 under hybridization conditions which only permit hybridization products to form which are fully complementary in the region of the mutation. For example, the present invention provides a nucleic acid probe which will hybridize to nucleic acid coding for a mutant KCNH2 polypeptide containing a mutation which causes short QT syndrome under conditions which only permit hybridization products to form which are fully complementary in the region causing said mutation, said mutation being caused by a mutation in said nucleic acid being a substitution of G for C or A for C at nucleotide position 1764, but will not hybridize to nucleic acid encoding wild type KCNH2 polypeptide. As used herein, “wild-type” or “WT” is the naturally occurring, non-mutant nucleic acid or protein.

The present invention also provides a method for diagnosing a polymorphism which causes short QT syndrome by hybridizing such a nucleic acid probe to a patient's sample of DNA or RNA under conditions which only permit hybridization products which are fully complementary in the region of the mutation to form, and determining the presence or absence of a signal indicating a hybridization product, the presence of a hybridization signal indicating the presence of short QT syndrome. Similarly, the present invention also provides a method for diagnosing a polymorphism which causes long QT syndrome by hybridizing such nucleic acid probes to a patient's sample of DNA or RNA under conditions which only permit hybridization products which are fully complementary in the region of the above described LQT syndrome mutations of SCN5A, KCNH2 or KCNQ1 to form, and determining the presence or absence of a signal indicating a hybridization product, the presence of a hybridization signal indicating the presence of long QT syndrome. Similarly, the present invention also provides a method for diagnosing a polymorphism which causes Brugada syndrome by hybridizing such nucleic acid probes to a patient's sample of DNA or RNA under conditions which only permit hybridization products which are fully complementary in the region of the above described Brugada syndrome mutations of SCN5A to form, and determining the presence or absence of a signal indicating a hybridization product, the presence of a hybridization signal indicating the presence of Brugada syndrome. Similarly, the present invention also provides a method for diagnosing a polymorphism which causes progressive conduction disease by hybridizing such a nucleic acid probe to a patient's sample of DNA or RNA under conditions which only permit hybridization products which are fully complementary in the region of the above described progressive conduction disease mutation of SCN5A to form, and determining the presence or absence of a signal indicating a hybridization product, the presence of a hybridization signal indicating the presence of long QT syndrome In one embodiment, the patient's DNA or RNA may be amplified and the amplified DNA or RNA is hybridized with said probes. The hybridization maybe performed in situ. A single-stranded conformation polymorphism technique may be used to assay for any of said mutations.

The present invention also provides a method for diagnosing a polymorphism which causes short QT syndrome, said polymorphism being a mutation substituting a lysine at residue 588 of the KCNH2 polypeptide, said method including using a single-stranded conformation polymorphism technique to assay for said polymorphism. The present invention also provides a method for diagnosing a polymorphism which causes Brugada syndrome, said polymorphism being at least one of the following mutations of the SCN5A polypeptide: R104W, R179 stop, T220I, G400A, E446K, F532C, A735V, R878C, H886P, L917R, E1573K, C1727R, V232I+L1307F, P336L+I1659V, Y1614 stop, deletion from E1573-G1604, and insertion of TG at 851, said method including using a single-stranded conformation polymorphism technique to assay for said polymorphism. The present invention also provides a method for diagnosing a polymorphism which causes LQT syndrome, said polymorphism being at least one of the following mutations: G189W in the KCNQ1 protein; with respect to the KCNH2 protein, R356H, a C deletion at 764, and a W398stop codon; and S1134I of the SCN5A protein, said method including using a single-stranded conformation polymorphism technique to assay for said polymorphism. The present invention also provides a method for diagnosing a polymorphism which causes progressive conduction disease, said polymorphism being a mutation substituting a serine for proline at residue 1008 of the SCN5A polypeptide, said method including using a single-stranded conformation polymorphism technique to assay for said polymorphism.

The present invention also provides a method for diagnosing a polymorphism which causes short QT syndrome comprising identifying a mismatch between a patient's DNA or RNA and a wild-type DNA or RNA probe wherein said probe hybridizes to the region of DNA encoding amino acid residue 588 of the KCNH2 polypeptide. The mismatch may be identified by an RNase assay wherein the patient's DNA or RNA, has been amplified and said amplified DNA or RNA, is hybridized with said probe. The hybridization may be performed in situ. The present invention also provides a method for diagnosing a polymorphism which causes Brugada syndrome comprising identifying a mismatch between a patient's DNA or RNA and wild-type DNA or RNA probes wherein said probes hybridize to the region of DNA encoding any of the following amino acid residues: 104, 179, 220, 400, 446, 532, 735, 878, 886, 917, 1573, 1727, 232, 130, 336, 1659 1614, 851 and 1573-1604 of the SCN5A polypeptide. The mismatch may be identified by an RNase assay wherein the patient's DNA or RNA, has been amplified and said amplified DNA or RNA, is hybridized with said probe. The hybridization may be performed in situ. The present invention also provides a method for diagnosing a polymorphism which causes long QT syndrome comprising identifying a mismatch between a patient's DNA or RNA and wild-type DNA or RNA probes wherein said probes hybridize to the region of DNA encoding any of the following amino acid residues: 189 in the KCNQ1 protein; 365, 398, and 764 in the KCNH2 protein; and 1134 of the SCN5A protein. The mismatch may be identified by an RNase assay wherein the patient's DNA or RNA, has been amplified and said amplified DNA or RNA, is hybridized with said probe. The hybridization may be performed in situ. The present invention also provides a method for diagnosing a polymorphism which causes progressive conduction disease comprising identifying a mismatch between a patient's DNA or RNA and a wild-type DNA or RNA probe wherein said probe hybridizes to the region of DNA encoding amino acid residue 1008 of the SCN5A polypeptide. The mismatch may be identified by an RNase assay wherein the patient's DNA or RNA, has been amplified and said amplified DNA or RNA, is hybridized with said probe. The hybridization may be performed in situ.

Also provided is a method for diagnosing a polymorphism which causes short QT syndrome which includes amplifying the region of the KCNH2 DNA or RNA surrounding and including base position 1764, and determining whether a C to A or a C to G substitution at position 1764 exists, said alteration being indicative of short QT syndrome. The present invention also provides a method for diagnosing a polymorphism which causes short QT syndrome by amplifying the region of the KCNH2 DNA or RNA encoding amino acid 588 of the KCNH2 polypeptide and sequencing the amplified DNA or RNA wherein substitution of nucleic acid encoding lysine at position 588 is indicative of short QT syndrome. Polymorphisms can lead to subclinical forms of each of these syndromes, which may manifest only after exposure to certain drugs or environmental factors. As such, the identification of a polymorphism allows practitioners to counsel patients to avoid these drugs or environmental factors.

Also provided is an isolated nucleic acid coding for a mutant KCNH2 polypeptide which causes short QT syndrome. In one embodiment, the nucleic acid encodes a mutant KCNH2 polypeptide containing a substitution of lysine for asparagine at position 588. In one embodiment, the DNA coding for a mutant KCNH2 polypeptide contains a substitution of either G or A for C at nucleotide position 1764 of the wild-type KCNH2 gene. A vector containing such isolated nucleic acid is also provided. A cell transformed or transfected with such isolated nucleic acid is also provided. Also provided is a nucleic acid probe which will hybridize to said isolated nucleic acid. Also provided is an isolated mutant KCNH2 polypeptide containing a substitution of lysine for asparagine at position 588.

Also provided is an isolated nucleic acid coding for a mutant SCN5A polypeptide having at least one of the following mutations: R104W, R179 stop, T220I, G400A, E446K, F532C, A735V, R878C, H886P, L917R, E1573K, C1727R, V232I+L1307F, P336L+I1659V, Y1614 stop, deletion from E1573-G1604, and insertion of TG at 851, and which causes Brugada syndrome. In one embodiment, the DNA coding for a mutant SCN5A protein contains at least one nucleotide substitution in the wild-type SCN5A gene as follows: t5179c (C1727R), c310t (R104W), insert of tg at 2550 (TG851), c2632t (R878C), t1595g (F532C), t2790g (L917R), c2204t (A735V), g4717a (E1573K), c535t (R179 stop), g1336a (E446K), g1199c (G400A),a2675c (H886P), c4842g (Y1614 stop), c659t (T2201), g694a+c3919t (V232I+L1307F), splice of exons 27 and 28=4810+7 ins GGG (E1573-G1604 deletion), and c1007t+a4975g (P336L+I1659V). Vectors containing such isolated nucleic acid are also provided. Cells transformed or transfected with such isolated nucleic acid are also provided. Also provided are a nucleic acid probes which will hybridize to said isolated nucleic acid. Also provided is an isolated mutant SCN5A polypeptide containing at least one of the following mutations: R104W, R179 stop, T220I, G400A, E446K, F532C, A735V, R878C, H886P, L917R, E1573K, C1727R, V232I+L1307F, P336L+I1659V, Y1614 stop, deletion from E1573-G1604, and insertion of TG at 851.

Also provided is an isolated nucleic acid coding for a KCNQ1 protein mutant G189W which causes LQT syndrome. In one embodiment, the DNA coding for a mutant KCNQ1 protein contains a g165t nucleotide substitution in the wild-type KCNQ1 gene. A vector containing such isolated nucleic acid is also provided. A cell transformed or transfected with such isolated nucleic acid is also provided. Also provided is a nucleic acid probe which will hybridize to said isolated nucleic acid. Also provided is an isolated mutant KCNQ1 polypeptide containing a G189W mutation.

Also provided is an isolated nucleic acid coding for a mutant KCNH2 protein which causes LQT syndrome having at least one of the following mutations: R356H, a C deletion at 764, and a W398stop. In one embodiment, the DNA coding for a mutant KCNH2 protein contains at least one of the following mutations g1067a (R356H), c2291 deletion (C764 deletion), and g1193a (W398 stop) of the wild-type KCNH2 gene. Vectors containing such isolated nucleic acid are also provided. Cells transformed or transfected with such isolated nucleic acid are also provided. Also provided is a nucleic acid probe which will hybridize to said isolated nucleic acid. Also provided is an isolated mutant KCNH2 polypeptide containing at least one of the following mutations: R356H, a C deletion at 764, and a W398stop.

Also provided is an isolated nucleic acid coding for a mutant SCN5A protein which causes LQT syndrome having the following mutation: S1134I. In one embodiment, the DNA coding for a mutant SCN5A protein contains a nucleotide substitution of g3401t in the wild-type SCN5A gene. A vector containing such isolated nucleic acid is also provided. A cell transformed or transfected with such isolated nucleic acid is also provided. Also provided is a nucleic acid probe which will hybridize to said isolated nucleic acid. Also provided is an isolated mutant SCN5A polypeptide containing a S1134I mutation.

Also provided is an isolated nucleic acid coding for a mutant SCN5A protein which causes progressive conduction disease having the following mutation: P1008S, In one embodiment, the DNA coding for a mutant SCN5A protein contains a nucleotide substitution of c3022t in the wild-type SCN5A gene. A vector containing such isolated nucleic acid is also provided. A cell transformed or transfected with such isolated nucleic acid is also provided. Also provided is a nucleic acid probe which will hybridize to said isolated nucleic acid. Also provided is an isolated mutant SCN5A polypeptide containing a P1008S mutation.

“Isolated”, as used herein, means that the original material to which it refers was removed from the environment where it may have originally been found. “Isolated” material also includes material which may have originally been found in a native environment but was synthesized outside that native environment by artificial means. Such “isolated” materials may be combined with other materials. Thus, for example, an “isolated” nucleic acid is still considered to be “isolated” even if it is found in a self-replicating cell that is the progeny of a parent cell that was transformed or transfected with nucleic acid that was not native to that parent cell.

With respect to short QT syndrome, two families with hereditary short QT syndrome and a high incidence of ventricular arrhythmias and sudden cardiac death were studied. Analysis for the genetic mutation in these two families was performed. (Families 30-371 and 30-335) (FIG. 1). Highly informative chromosomal markers were used targeting loci containing 24 candidate genes involved in cardiac electrical activity to perform the initial haplotype analysis in family 30-371. Direct sequencing of the gene exons corresponding to the loci segregating with the affected individuals identified a missense mutation (C to A substitution at nucleotide 1764) in family 30-371 in KCNH2. Analysis of family 30-335 identified a different missense mutation in the same residue (C to G substitution at nucleotide 1764) in KCNH2. Both mutations substituted the asparagine at codon 588 in KCNH2 protein (HERG) for a positively charged lysine (FIG. 2). This residue corresponds to exon 7, which encodes the pore region of the IK_(r) channel. This residue is located in the S5-P loop region of HERG at the mouth of the channel. The mutation was present in all affected members in the respective family and in none of the unaffected. Given the pattern of transmission, it is believed that the mutation must have been present in two of the individuals who died suddenly in family 30-371 as obligate carriers. These mutations were not present in four hundred control chromosomes. A third family line with certain members exhibiting sudden cardiac death mortality was investigated and also found to have the N588K mutation in KCNH2 associated with SQT syndrome.

To determine the mechanism by which mutation N588K reduces the duration of the ventricular action potential and shortens the QT interval and to obtain current recordings representative of I_(Kr), the mutated KCNH2 channels (N588K) were co-expressed with the ancillary β-subunit KCNE2 (MiRP1) in human embryonic kidney cells (TSA201) and patch clamp experiments were performed. Whole cell recordings (FIG. 3 a) showed that the wild type (WT) HERG/KCNE2 currents elicited by sequential depolarizing pulses reached a maximum steady state current at −5 mV and started to decrease due to the rapid onset of inactivation (rectification) at more positive potentials. In cells transfected with the WT channels, the typical large tail currents generated by inactivated channels rapidly reopening (recovery) upon repolarization were also observed. In contrast, N588K/KCNE2 steady state current continued to increase linearly well over +40 mV and significant tail currents following repolarization were not observed. Analysis of the current voltage relationship (FIG. 3B) shows that N588K/KCNE2 currents did not rectify significantly in a physiological range of potentials.

To determine how the mutation altered the kinetics of the current during an action potential, WT and N588K currents were elicited using a stimulus generated by a previously recorded AP. FIG. 3C shows that WT currents displayed a “hump” like waveform with slow activation kinetics and a rapid increase during the repolarization phase of the action potential, as inactivated channels quickly recovered. In sharp contrast, N588K/KCNE2 currents displayed a dome-like configuration resulting in a much larger relative current during the initial phases of the action potential.

KCNH2 protein has a “shaker like” tetrameric structure composed of homologous core units each containing six membrane-spanning segments. Co-assembly with the beta-subunit MiRP1 (KCNE2) is required to fully reproduce the biophysical and pharmacological properties of the native I_(Kr). KCNH2 has previously been linked to a decrease in outward repolarizing current responsible for the hereditary (LQT2) and acquired forms of LQTS. A common polymorphism in KCNH2 (K897T) has been reported to produce a modest abbreviation of QTc to 388.5±2.9 by shifting the voltage of activation of I_(Kr) by −7 mV. KCNH2 is also the primary target of Class III antiarrhythmics. Binding of dofetilide and sotalol occurs primarily in the open state. The S5-P loop region of KCNH2 forms the pore of the channel and contains the selectivity filter. Chimeric studies of KCNH2 showed that replacing the S5-S6 linker, which contains the pore region, by the corresponding area from the bovine ether-a-go-go (BEAG) removes the high affinity block by dofetilide, indicating that this area contains residues important for binding of methanesulfonanilides and C type inactivation. Abolition of the current rectification by N588K further support the notion that residues in this area of the channel are important for C-type inactivation and binding of methanesulfonanilides to KCNH2. Block of I_(Kr) by methanesulfonanilides, phosphodiesterase inhibitors, macrolide antibiotics, antifungal agents and antihistamines is the basis for the QT prolonging effects and potential arrythmogenecity of these compounds.

Because QT abbreviation is likely due to a decrease in ventricular AP duration subsequent to an increase in repolarizing current, it was believed that blocking I_(Kr), with Class III antiarrhythmic drugs could be a potential therapeutic approach to the treatment of SQTS. FIG. 4 shows that Sotalol, a class III antiarrhythmic with potent I_(Kr) blocking actions, was administered as a preliminary test of this hypothesis. FIG. 4 illustrates the response of patient IV-5 of family 30-371 to 1 mg/kg IV sotalol. QTc at baseline was 291 msec and remained practically unchanged after sotalol, suggesting that this particular phenotype is not responsive to this dose of the I_(Kr) blocker. FIG. 5 shows that extracellular application of sotalol caused a shift in sensitivity of the KCNH2 channel by 20 fold as a consequence of the N588K mutation in TSA201 cells. IC₅₀ was shifted from 0.137 mM in WT to 2.82 mM in N588K. FIG. 6 shows that extracellular application of quinidine caused a shift in sensitivity of the KCNH2 channel by 5.8 fold as a consequence of the N588K mutation in TSA201 cells. IC₅₀ was shifted from 0.75 mM in WT to 4.35 mM in N588K. Accordingly, the N588K mutation produces less sensitivity of a decrease in sensitivity of KCNH2 to quinidine.

These results provide for the first time a genetic basis for the short QT syndrome, a disease characterized by marked abbreviation of the QT interval and a high incidence atrial and ventricular arrhythmias and sudden death. The data demonstrate the first linkage of a cardiac disease to a gain of function in KCNH2, which encodes for rapidly activating delayed rectifier current, I_(Kr). A N588K missense mutation is shown to abolish rectification of the current and reduce the affinity of the channel for drugs with Class III antiarrhythmic action. The net effect of the mutation is to increase the repolarizing currents active during the early phases of the AP, leading to abbreviation of the action potential, and thus to abbreviation of the QT interval. Because of the heterogeneous distribution of ion currents within the heart, it may be that the AP shortening in SQTS is heterogeneous, leading to accentuation of dispersion of repolarization and the substrate for the development of both atrial and ventricular arrhythmias. Given the young age of some patients (3 months), the data also provides evidence linking KCNH2 mutations to sudden infant death syndrome (SIDS). Since I_(Ks) contributes importantly to repolarization, block of this current may benefit SQT syndrome. Selective I_(Ks) blockers are under development, e.g., Chromanol 293B and HMR 1556. When compared to Chromanol 293B, HMR 1556 has a higher potency and specificity towards I_(Ks).

Accordingly, a method of screening compounds for use in treating cardiac ion channel abnormalities resulting from the mutations described herein is provided. In one aspect, patients who have been diagnosed with one or more of the mutations described herein are dosed with a pharmaceutically acceptable compound which an investigator suspects may have an effect on the ion channel, an electrocardiogram is taken, and the effect of the QT interval, if any, is ascertained. A therapeutic effect is considered one which modifies an abnormal interval to a more normal interval.

In another aspect, a cell based assay is provided. Cells containing nucleic acid encoding mutant KCNH2, SCN5A or KCNQ1 protein as described herein are contacted with a test compound and the effect on ion channel currents is ascertained. Suitable cells include, e.g., human embryonic kidney cells (HEK) and cardiac cell lines such as HL-1, described in U.S. Pat. No. 6,316,207, incorporated herein by reference. Other modalities include transfected oocytes or transgenic animals. A test compound is added to the cells in culture or administered to a transgenic animal containing mutant KCNH2, SCN5A or KCNQ1 and the effect on the current of the ion channel is compared to the current of a cell or animal containing the wild-type KCNH2, SCN5A or KCNQ1. Drug candidates which alter the current to a more normal level are useful for treating or preventing LQT syndrome, SQT syndrome, Brugada syndrome or progressive conduction disease.

FIG. 7 illustrates representative whole cell current recordings for WT (Panel A) and SCN5A F532C Brugada syndrome mutant (Panel B) in transfected TSA201 cells. Current recordings were obtained at test potentials between −100 and 0 mV in 5 mV increments from a holding potential of −120 mV. Panel C: Normalized I-V relation for WT (n=9) and F532C (n=9) channels. Panel D: Steady state-activation relation for WT and F532C. Chord conductance was determined using the ratio of current to the electromotive potential for the 9 cells shown in Panel C. Data were normalized and plotted against their test potential.

FIG. 8 illustrates representative steady-state inactivation recordings for WT (Panel A) and SCN5A F532C (Panel B) observed in response to the voltage clamp protocol (top of figure). Panel C: Peak current was normalized to their respective maximum values and plotted against the conditioning potential. The steady state inactivation relation measured with the F532C mutation shows a −10 mV shift of mid-inactivation voltage in the hyperpolarizing direction (−102.4±4.8; n=9 versus −92.3±2.4 for WT; n=10; P<0.05). Thus, a major loss of function of sodium channel current is expected consistent with the phenotype of the disease. Such a shift would be expected to lead to a reduced sodium channel current due to reduced availability of sodium channels at the normal resting potential.

According to the diagnostic and prognostic methods of the present invention, alteration of the wild-type KCNH2, KCNQ1, and/or SCN5A genes and/or proteins are detected. Useful diagnostic techniques include, but are not limited to fluorescent in situ hybridization (FISH), direct nucleic acid sequencing, PFGE analysis, Southern blot analysis, single stranded conformation analysis (SSCA), RNase protection assay, allele-specific oligonucleotide (ASO), dot blot analysis, hybridization using nucleic acid modified with gold nanoparticles and PCR-SSCP. Also useful is the recently developed technique of DNA microarray technology. Implementation of these techniques is considered to be routine for those skilled in the art.

The presence of sudden cardiac death or susceptibility thereto may be ascertained by testing any tissue of a human subject or non-human subject for mutations of the KCNH2, KCNQ1, and/or SCN5A genes as described herein. For example, a person who has inherited a germline KCNH2, KCNQ1, and/or SCN5A mutation as described herein would be prone have SQT syndrome, LQT syndrome, Brugada syndrome, progressive transmission disease, to develop arrhythmias or suffer from sudden cardiac death depending on the particular mutation. This can be determined by testing DNA from any tissue of the subject's body. Most simply, blood can be drawn and DNA extracted from the cells of the blood. In addition, prenatal diagnosis can be accomplished by testing fetal cells, placental cells or amniotic cells for mutations of the KCNH2, KCNQ1, and/or SCN5A genes. Alteration of a wild-type KCNH2, KCNQ1, and/or SCN5A genes, whether, for example, by point mutation or deletion, can be detected by any of the means discussed herein.

Those skilled in the art are familiar with numerous methods that can be used to detect DNA sequence variation. Direct DNA sequencing, either manual sequencing or automated fluorescent sequencing can detect sequence variation. Another approach is the single-stranded conformation polymorphism assay (SSCP) (Orita et al., Proc. Natl. Acad. Sci. USA 86:2766-2770 (1989)). This method does not detect all sequence changes, especially if the DNA fragment size is greater than 200 bp, but can be optimized to detect most DNA sequence variation. The reduced detection sensitivity may be a disadvantage, but the increased throughput possible with SSCP can make it an attractive, viable alternative to direct sequencing for mutation detection. The fragments which have shifted mobility on SSCP gels are then sequenced to determine the exact nature of the DNA sequence variation. Other approaches based on the detection of mismatches between the two complementary DNA strands include clamped denaturing gel electrophoresis (CDGE) (Sheffield et al., Am. J. Hum. Genet. 49:699-706 (1991)), heteroduplex analysis (HA) (White et al., Genomics 12:301-306 (1992)) and chemical mismatch cleavage (CMC) (Grompe et al., Proc. Natl. Acad. Sci. USA 86:5855-5892 (1989)). Once a mutation is known, an allele specific detection approach such as allele specific oligonucleotide (ASO) hybridization can be utilized to rapidly screen large numbers of other samples for that same mutation. Such a technique can utilize probes which are labeled with gold nanoparticles to yield a visual color result (Elghanian et al., Science 277:1078-1081 (1997)).

Detection of point mutations described herein may be accomplished by molecular cloning of the KCNH2, KCNQ1, and/or SCN5A genes and sequencing the genes using techniques well known in the art. Also, the gene or portions of the gene may be amplified, e.g., by PCR or other amplification technique, and the amplified gene or amplified portions of the gene may be sequenced.

Well known methods for indirect, test for confirming the presence of a susceptibility mutant include: 1) single stranded conformation analysis (SSCP) (Orita M, et al. (1989) Proc. Natl. Acad. Sci. USA 86:2766-2770); 2) denaturing gradient gel electrophoresis (DGGE) (Wartell R M, et al. (1990) Nucl. Acids Res. 18:2699-2705; Sheffield V C, et al. (1989) Proc. Natl. Acad. Sci. USA 86:232-236); 3) RNase protection assays (Finkelstein J, et al. (1990) Genomics 7:167-172; Kinszler K W, et al. (1991) Science 251:1366-1370); 4) allele-specific oligonucleotides (ASOs) (Conner B J, et al. (1983) Proc. Natl. Acad. Sci. USA 80:278-282); 5) the use of proteins which recognize nucleotide mismatches, such as the E. coli mutS protein (Modrich P (1991) Ann. Rev. Genet. 25:229-253); and 6) allele-specific PCR (Ruano G and Kidd K K (1989) Nucl. Acids Res. 17:8392). For allele-specific PCR, primers are used which hybridize at their 3′ ends to particular KCNH2, KCNQ1, and/or SCN5A gene mutations. If the particular mutation is not present, an amplification product is not observed. Amplification Refractory Mutation System (ARMS) can also be used. In addition, restriction fragment length polymorphism (RFLP) probes for the genes or surrounding marker genes can be used to score alteration of an mutant or an insertion in a polymorphic fragment. Such a method is useful for screening relatives of an affected individual for the presence of the mutation found in that individual. Other techniques for detecting insertions and deletions as known in the art can be used.

In the first three methods (SSCP, DGGE and RNase protection assay), a new electrophoretic band appears. SSCP detects a band which migrates differentially because the sequence change causes a difference in single-strand, intramolecular base pairing. RNase protection involves cleavage of the mutant polynucleotide into two or more smaller fragments. DGGE detects differences in migration rates of mutant sequences compared to wild-type sequences, using a denaturing gradient gel. In an allele-specific oligonucleotide assay, an oligonucleotide is designed which detects a specific sequence, and the assay is performed by detecting the presence or absence of a hybridization signal. In the mutS assay, the protein binds only to sequences that contain a nucleotide mismatch in a heteroduplex between mutant and wild-type sequences. Mismatches, according to the present invention, are hybridized nucleic acid duplexes in which the two strands are not 100% complementary. Lack of total homology may be due to deletions, insertions, inversions or substitutions. Mismatch detection can be used to detect point mutations in the gene or in its mRNA product. While these techniques are less sensitive than sequencing, they are simpler to perform on a large number of samples. An example of a mismatch cleavage technique is the RNase protection method. The method involves the use of a labeled riboprobe which is complementary to the respective human wild-type KCNH2, KCNQ1, and/or SCN5A gene coding sequences. The riboprobe and either MRNA or DNA isolated from the subject are annealed (hybridized) together and subsequently digested with the enzyme RNase A which is able to detect some mismatches in a duplex RNA structure. If a mismatch is detected by RNase A, it cleaves at the site of the mismatch. Thus, when the annealed RNA preparation is separated on an electrophoretic gel matrix, if a mismatch has been detected and cleaved by RNase A, an RNA product will be seen which is smaller than the full length duplex RNA for the riboprobe and the mRNA or DNA. The riboprobe need not be the full length of the mRNA or gene but can be a segment of either. If the riboprobe comprises only a segment of the MRNA or gene, it will be desirable to use a number of these probes to screen the whole MRNA sequence for mismatches.

In similar fashion, DNA probes can be used to detect mismatches, through enzymatic or chemical cleavage. See, e.g., Cotton R G, et al. (1988) Proc. Natl. Acad. Sci. USA 85:4397-4401; Shenk T E, et al. (1975) Proc. Natl. Acad. Sci. USA 72:989-993; Novack D F, et al. (1986) Proc. Natl. Acad. Sci USA 83:586-590. Alternatively, mismatches can be detected by shifts in the electrophoretic mobility of mismatched duplexes relative to matched duplexes. See, e.g., Cariello N F (1988) Am. J. Human Genetics 42:726-734). With either riboprobes or DNA probes, the cellular mRNA or DNA which might contain a mutation can be amplified using PCR before hybridization. Changes in DNA of the KCNH2, KCNQ1, and/or SCN5A genes can also be detected using Southern hybridization.

DNA sequences of the KCNH2, KCNQ1, and/or SCN5A genes which have been amplified by use of PCR may also be screened using mutant-specific probes. These probes are nucleic acid oligomers, each of which contains a region of the gene sequence harboring any of the mutations described herein. For example, one oligomer may be about 30 nucleotides in length, corresponding to a portion of the gene sequence. By use of a battery of such probes, PCR amplification products can be screened to identify the presence of a previously identified mutation in the gene. Hybridization of probes with amplified KCNH2, KCNQ1, and/or SCN5A sequences can be performed, for example, on a nylon filter. Hybridization to a particular probe under high stringency hybridization conditions indicates the presence of the same mutation in the tissue as in the allele-specific probe. High stringency hybridization conditions may be defined as those conditions which allow an 8 basepair stretch of a first nucleic acid (a probe) to bind to a 100% perfectly complementary 8 basepair stretch of nucleic acid while simultaneously preventing binding of said first nucleic acid to a nucleic acid which is not 100% complementary, i.e., binding will not occur if there is a mismatch.

Thus, in one embodiment, the above-identified DNA sequences may be detected by DNA hybridization probe technology. In one example, which is not exclusive, the sample suspected of containing the genetic marker is spotted directly on a series of membranes and each membrane is hybridized with a different labeled oligonucleotide probe that is specific for the particular sequence variation. One procedure for spotting the sample on a membrane is described by Kafotos et al., Nucleic Acids Research, 7:1541-1552 (1979).

Briefly, the DNA sample affixed to the membrane may be pretreated with a prehybridization solution containing sodium dodecyl sulfate, Ficoll, serum albumin and various salts prior to the probe being added. Then, a labeled oligonucleotide probe that is specific to each sequence to be detected is added to a hybridization solution similar to the prehybridization solution. The hybridization solution is applied to the membrane and the membrane is subjected to hybridization conditions that will depend on the probe type and length, type and concentration of ingredients, etc. Generally, hybridization may be carried out at about 25-75° C., preferably 35 to 65° C., for 0.25-50 hours, preferably less than three hours. The greater the stringency of conditions, the greater the required complementarity for hybridization between the probe and sample. If the background level is high, stringency may be increased accordingly. The stringency can also be incorporated in the wash.

After the hybridization the sample is washed of unhybridized probe using any suitable means such as by washing one or more times with varying concentrations of standard saline phosphate EDTA (SSPE) (180 nM NaCl, 10 mM Na₂ HPO₄ and 1 M EDTA, pH 7.4) solutions at 25-75° C. for about 10 minutes to one hour, depending on the temperature. The label is then detected by using any appropriate detection techniques known to those skilled in the art.

The sequence-specific oligonucleotide that may be employed herein is an oligonucleotide that may be prepared using any suitable method, such as, for example, the organic synthesis of a nucleic acid from nucleoside derivatives. This synthesis may be performed in solution or on a solid support. One type of organic synthesis is the phosphotriester method, which has been utilized to prepare gene fragments or short genes. In the phosphotriester method, oligonucleotides are prepared that can then be joined together to form longer nucleic acids. For a description of this method, see, e.g., Narang, S. A., et al., Meth. Enzymol., 68, 90 (1979) and U.S. Pat. No. 4,356,270.

A second type of organic synthesis is the phosphodiester method, which has been utilized to prepare tRNA genes. See Brown, E. L., et al., Meth. Enzymol., 68, 109 (1979) for a description of this method. As in the phosphotriester method, the phosphodiester method involves synthesis of oligonucleotides that are subsequently joined together to form the desired nucleic acid.

Automated embodiments of these methods may also be employed. In one such automated embodiment diethylphosphoramidites are used as starting materials and may be synthesized as described by Beaucage et al., Tetrahedron Letters, 22:1859-1862 (1981). One method for synthesizing oligonucleotides on a modified solid support is described, e.g., in U.S. Pat. No. 4,458,066. It is also possible to use a primer which has been isolated from a biological source (such as a restriction endonuclease digest).

The sequence-specific oligonucleotide must encompass the region of the sequence which spans the nucleotide variation being detected and must be specific for the nucleotide variation being detected. For example, oligonucleotides may be prepared, each of which contains the nucleotide sequence site characteristic of each of the mutated DNA sequences herein. Each oligonucleotide would be hybridized to duplicates of the same sample to determine whether the sample contains one or more of the regions of the locus where the mutations described herein may occur which are characteristic of LQT syndrome, SQT syndrome, Brugada syndrome and progressive conduction disease.

The length of the sequence-specific oligonucleotide will depend on many factors, including the source of oligonucleotide and the nucleotide composition. For purposes herein, the oligonucleotide typically contains 15-30 nucleotides, although it may contain more or fewer nucleotides. While oligonucleotides which are at least 19-mers in length may enhance specificity and/or sensitivity, probes which are less than 19-mers, e.g., 16-mers, show more sequence-specific discrimination, presumably because a single mismatch is more destabilizing. If amplification of the sample is carried out as described below prior to detection with the probe, amplification increases specificity so that a longer probe length is less critical, and hybridization and washing temperatures can be lowered for the same salt concentration. Therefore, in such a case it may be preferred to use probes which are less than 19-mers.

Where the sample is first placed on the membrane and then detected with the oligonucleotide, the oligonucleotide should be labeled with a suitable label moiety, which may be detected by spectroscopic, photochemical, biochemical, immunochemical or chemical means. Immunochemical means include antibodies which are capable of forming a complex with the oligonucleotide under suitable conditions, and biochemical means include polypeptides or lectins capable of forming a complex with the oligonucleotide under the appropriate conditions. Examples include fluorescent dyes, electron-dense reagents, enzymes capable of depositing insoluble reaction products or being detected chronogenically, such as alkaline phosphatase, a radioactive label such as ³²P, or biotin. If biotin is employed, a spacer arm may be utilized to attach it to the oligonucleotide.

In a “reverse” dot blot format, a labeled sequence-specific oligonucleotide probe capable of hybridizing with one of the DNA sequences is spotted on (affixed to) the membrane under prehybridization conditions as described above. The sample is then added to the pretreated membrane under hybridization conditions as described above. Then the labeled oligonucleotide or a fragment thereof is released from the membrane in such a way that a detection means can be used to determine if a sequence in the sample hybridized to the labeled oligonucleotide. The release may take place, for example, by adding a restriction enzyme to the membrane which recognizes a restriction site in the probe. This procedure, known as oligomer restriction, is described more fully in EP Patent Publication 164,054 published Dec. 11, 1985, the disclosure of which is incorporated herein by reference.

Alternatively, a sequence specific oligonucleotide immobilized to the membrane could bind or “capture” a target DNA strand (PCR-amplified). This “captured” strand could be detected by a second labeled probe. The second oligonucleotide probe could be either locus-specific or allele-specific.

In an alternative method for detecting the DNA sequences herein, the sample to be analyzed is first amplified using DNA polymerase, nucleotide triphosphates and primers. Briefly, this amplification process involves the steps of:

(a) treating a DNA sample suspected of containing one or more of the mutations described above, together or sequentially, with different nucleotide triphosphates, an agent for polymerization of the nucleotide triphosphates, and one deoxyribonucleotide primer for each strand of each DNA suspected of containing the abode described mutations under hybridizing conditions, such that for each DNA strand containing each different genetic marker to be detected, an extension product of each primer is synthesized which is complementary to each DNA strand, wherein said primer(s) are selected so as to be substantially complementary to each DNA strand containing each different genetic marker, such that the extension product synthesized from one primer, when it is separated from its complement, can serve as a template for synthesis of the extension product of the other primer; (b) treating the sample under denaturing conditions to separate the primer extension products from their templates if the sequence(s) to be detected are present; and (c) treating the sample, together or sequentially, with the nucleotide triphosphates, an agent for polymerization of the nucleotide triphosphates, and oligonucleotide primers such that a primer extension product is synthesized using each of the single strands produced in step (b) as a template, wherein steps (b) and (c) are repeated a sufficient number of times to result in detectable amplification of the nucleic acid containing the sequence(s) if present.

The sample is then affixed to a membrane and detected with a sequence-specific probe as described above. Preferably, steps (b) and (c) are repeated at least five times, and more preferably 15-30 times if the sample contains human genomic DNA. If the sample comprises cells, preferably they are heated before step (a) to expose the DNA therein to the reagents. This step avoids extraction of the DNA prior to reagent addition.

In a “reverse” dot blot format, at least one of the primers and/or at least one of the nucleotide triphosphates used in the amplification chain reaction is labeled with a detectable label, so that the resulting amplified sequence is labeled. These labeled moieties may be present initially in the reaction mixture or added during a later cycle. Then an unlabeled sequence-specific oligonucleotide capable of hybridizing with the amplified sequence(s), if the sequence(s) is/are present, is spotted on (affixed to) the membrane under prehybridization conditions as described above. The amplified sample is then added to the pretreated membrane under hybridization conditions as described above. Finally, detection means are used to determine if an amplified sequence in the DNA sample has hybridized to the oligonucleotide affixed to the membrane. Hybridization will occur only if the membrane-bound sequence containing the variation is present in the amplification product.

Variations of this method include use of an unlabeled PCR target, an unlabeled immobilized allele-specific probe and a labeled oligonucleotide probe in a sandwich assay.

The amplification method provides for improved specificity and sensitivity of the probe; an interpretable signal can be obtained with a 0.04 μg sample in six hours. Also, if the amount of sample spotted on a membrane is increased to 0.1-0.5 μg, non-isotopically labeled oligonucleotides may be utilized in the amplification process rather than the radioactive probes used in previous methods. Finally, as mentioned above, the amplification process may be applicable to use of sequence-specific oligonucleotides less than 19-mers in size, thus allowing use of more discriminatory sequence-specific oligonucleotides.

In a variation of the amplification procedure, a thermostable enzyme, such as one purified from Thermus aquaticus, may be utilized as the DNA polymerase in a temperature-cycled chain reaction. The thermostable enzyme refers to an enzyme which is stable to heat and is heat resistant and catalyzes (facilitates) combination of the nucleotides in the proper manner to form the primer extension products that are complementary to each DNA strand.

In this latter variation of the technique, the primers and nucleotide triphosphates are added to the sample, the mixture is heated and then cooled, and then the enzyme is added, the mixture is then heated to about 90-100° C. to denature the DNA and then cooled to about 35-40° C., and the cycles are repeated until the desired amount of amplification takes place. This process may also be automated. The amplification process using the thermostable enzyme is described more fully in U.S. Pat. No. 4,965,188, which is incorporated herein by reference.

The invention herein also contemplates a kit format which includes a packaged multicontainer unit having containers for each labeled sequence-specific DNA probe. The kit may optionally contain a means to detect the label (such as an avidin-enzyme conjugate and enzyme substrate and chromogen if the label is biotin). In addition, the kit may include a container that has a positive control for the probe containing one or more DNA strands with the sequence to be detected and a negative control for the probe that does not contain the DNA strands having any of the sequences to be detected.

Nucleic acid analysis via microarray technology is also applicable to the present invention. In this technique, literally thousands of distinct oligonucleotide probes are built up in an array on a silicon chip. Nucleic acid to be analyzed labeled, e.g., fluorescently, and hybridized to the probes on the chip. It is also possible to study nucleic acid-protein interactions using these nucleic acid microarrays. Using this technique one can determine the presence of mutations or even sequence the nucleic acid being analyzed or one can-measure expression levels of a gene of interest. The method is one of parallel processing of many, even thousands, of probes at once and can tremendously increase the rate of analysis.

One method for detecting the amino acid sequences in a protein sample that are associated with LQT syndrome, SQT syndrome, Brugada syndrome and progressive conduction disease as described herein involves the use of an immunoassay employing one or more antibodies that bind to one or more of the mutated amino acid sequences. While the antibodies may be polyclonal or monoclonal, monoclonal antibodies are preferred in view of their specificity and affinity for the antigen.

Polyclonal antibodies may be prepared by well-known methods which involve synthesizing a peptide containing one or more of the amino acid sequences described herein as associated with LQT syndrome, SQT syndrome, Brugada syndrome and progressive conduction disease, purifying the peptide, attaching a carrier protein to the peptide by standard techniques, and injecting a host such as a rabbit, rat, goat, mouse, etc. with the peptide. The sera are extracted from the host by known methods and screened to obtain polyclonal antibodies which are specific to the peptide immunogen. The peptide may be synthesized by the solid phase synthesis method described by Merrifield, R. B., Adv. Enzymol. Relat. Areas Mol. Biol., 32:221-296 (1969) and in “The Chemistry of Polypeptides” (P. G. Katsoyannis, ed.), pp. 336-361, Plenum, New York (1973), the disclosures of which are incorporated herein by reference. The peptide is then purified and may be conjugated to keyhold limpet hemocyanin (KLH) or bovine serum albumin (BSA). This may be accomplished via a sulhydryl group, if the peptide contains a cysteine residue, using a heterobifunctional crosslinking reagent such as N-maleimido-6-amino caproyl ester of 1-hydroxy-2-nitrobenzene-4-sulfonic acid sodium salt.

The monoclonal antibody will normally be of rodent or human origin because of the availability of murine, rat, and human tumor cell lines that may be used to produce immortal hybrid cell lines that secrete monoclonal antibody. The antibody may be of any isotype, but is preferably an IgG, IgM or IgA, most preferably an IgG2a.

The murine monoclonal antibodies may be produced by immunizing the host with the peptide mentioned above. The host may be inoculated intraperitoneally with an immunogenic amount of the peptide and then boosted with similar amounts of the immunogenic peptide. Spleens or lymphoid tissue is collected from the immunized mice a few days after the final boostand a cell suspension is prepared therefrom for use in the fusion.

Hybridomas may be prepared from the splenocytes or lymphoid tissue and a tumor (myeloma) partner using the general somatic cell hybridization technique of Koehler, B. and Milstein, C., Nature, 256:495-497 (1975) and of Koehler, B. et al., Eur. J. Immunol., 6:511-519 (1976). Suitable myeloma cells for this purpose are those which fuse efficiently, support stable, high-level expression of antibody by the selected antibody-producing cells, and are sensitive to a medium such as HAT medium. Among these, suitable myeloma cell lines are murine myeloma lines, such as those derived from MOPC-21 and MOPC-11 mouse tumors available from the Salk Institute, Cell Distribution Center, San Diego, Calif., USA, or P3X63-Ag8.653 (653) and Sp2/0-Ag14 (SP2/0) myeloma lines available from the American Type Culture Collection, Rockville, Md., USA, under ATCC CRL Nos. 1580 and 1581, respectively.

Basically, the technique may involve fusing the appropriate tumor cells and splenocytes or lymphoid tissue using a fusogen such as polyethylene glycol. After the fusion the cells are separated from the fusion medium and grown on a selective growth medium, such as HAT medium, to eliminate unhybridized parent cells and to select only those hybridomas that are resistant to the medium and immortal. The hybridomas may be expanded, if desired, and supernatants may be assayed by conventional immunoassay procedures (e.g., radioimmunoassay, enzyme immunoassay, or fluorescence immunoassay) using the immunizing agent as antigen. Positive clones may be characterized further to determine whether they meet the criteria of the antibodies of the invention. For example, the antigen-binding ability of the antibodies may be evaluated in vitro by immunoblots, ELISAs and antigen neutralizing tests.

An example of a suitable procedure for making a hybrid cell line that secretes human antibodies against the amino acid genetic markers is somatic cell hybridization using a mouse×human parent hybrid cell line and a human cell line producing sufficiently high levels of such antibodies. The human cell line may be obtained from volunteers immunized with the peptide(s) described above. The human cell line may be transformed with Epstein-Barr virus (EBV) as described, for example, by Foung, et al., J. Immunol. Methods, 70:83-90 (1984).

When EBV transformation is employed, the most successful approaches have been either to pre-select the population of B cells to be transformed or to post-select the antigen-specific transformed populations by panning or rosetting techniques, as described by Kozbar, et al., Scan. J. Immunol., 10:187-194 (1979) and Steinitz, et al., J. Clin. Lab. Immun., 2:1-7 (1979). EBV transformation has been combined with cell fusion to generate human monoclonal antibodies (see, e.g., Foung et al., J. Immun. Meth., 70:83-90 (1984)), due to instability of immunoglobulin secretion by hybridomas when compared to EBV lymphoblastoid cell lines, and higher frequencies of rescue of the antigen-specific populations. EBV most frequently infects and transforms IgM-bearing B cells, but B cells secreting other classes of Ig can also be made into long-term lines using the EBV fusion technique, as described by Brown and Miller, J. Immunol., 128:24-29 (1982).

The cell lines which produce the monoclonal antibodies may be grown in vitro in suitable culture medium such as Iscove's medium, Dulbecco's Modified Eagle's Medium, or RPMI-1640 medium from Gibco, Grand Island, N.Y., or in vivo in syngeneic or immunodeficient laboratory animals. If desired, the antibody may be separated from the culture medium or body fluid, as the case may be, by conventional techniques such as ammonium sulfate precipitation, hydroxyapatite chromatography, ion exchange chromatography, affinity chromatography, electrophoresis, microfiltration, and ultracentrifugation.

The antibodies herein may be used to detect the presence or absence of one or more of the amino acid mutations described herein as associated with LQT syndrome, SQT syndrome, Brugada syndrome and progressive conduction disease. The cells may be incubated in the presence of the antibody, and the presence or absence and/or degree of reaction (antibody-peptide binding) can be determined by any of a variety of methods used to determine or quantitate antibody/antigen interactions (e.g., fluorescence, enzyme-linked immunoassay (ELISA), and cell killing using antibody and complement by standard methods). The antibody employed is preferably a monoclonal antibody.

For use in solid phase immunoassays, the antibodies employed in the present invention can be immobilized on any appropriate solid test support by any appropriate technique. The solid test support can be any suitable insoluble carrier material for the binding of antibodies in immunoassays. Many such materials are known in the art, including, but not limited to, nitrocellulose sheets or filters; agarose, resin, plastic (e.g., PVC or polystyrene) latex, or metal beads; plastic vessels; and the like. Many methods of immobilizing antibodies are also known in the art. See, e.g., Silman et al., Ann. Rev. Biochem., 35:873 (1966); Melrose, Rev. Pure & App. Chem., 21:83 (1971); Cuatrecafas, et al., Meth. Enzym., Vol. 22 (1971). Such methods include covalent coupling, direct adsorption, physical entrapment, and attachment to a protein-coated surface. In the latter method, the surface is first coated with a water-insoluble protein such as zein, collagen, fibrinogen, keratin, glutelin, etc. The antibody is attached by simply contacting the protein-coated surface with an aqueous solution of the antibody and allowing it to dry.

Any combination of support and binding technique which leaves the antibody immunoreactive, yet sufficiently immobilizes the antibody so that it can be retained with any bound antigen during a washing, can be employed in the present invention. A preferred solid test support is a plastic bead.

In the sandwich immunoassay, a labeled antibody is employed to measure the amount of antigen bound by the immobilized monoclonal antibody. The label can be any type that allows for the detection of the antibody when bound to a support. Generally, the label directly or indirectly results in a signal which is measurable and related to the amount of label present in the sample. For example, directly measurable labels can include radiolabels (e.g., ¹²⁵I, ³⁵S, ¹⁴C, etc.). A preferred directly measurable label is an enzyme, conjugated to the antibody, which produces a color reaction in the presence of the appropriate substrate (e.g., horseradish peroxidase/o-phenylenediamine). An example of an indirectly measurable label would be antibody that has been biotinylated. The presence of this label is measured by contacting it with a solution containing a labeled avidin complex, whereby the avidin becomes bound to the biotinylated antibody. The label associated with the avidin is then measured. A preferred example of an indirect label is the avidin/biotin system employing an enzyme conjugated to the avidin, the enzyme producing a color reaction as described above. It is to be understood, however, that the term “label” is used in its broadest sense and can include, for example, employing “labeled” antibodies where the label is a xenotypic or isotypic difference from the immobilized antibody, so that the presence of “labeled” antibodies is detectable by incubation with an anti-xenotypic or anti-isotypic antibody carrying a directly detectable label.

Whatever label is selected, it results in a signal which can be measured and is related to the amount of label in a sample. Common signals are radiation levels (when radioisotopes are used), optical density (e.g., when enzyme color reactions are used), and fluorescence (when fluorescent compounds are used). It is preferred to employ a nonradioactive signal, such as optical density (or color intensity) produced by an enzyme reaction. Numerous enzyme/substrate combinations are known in the immunoassay art which can produce a suitable signal. See, e.g., U.S. Pat. Nos. 4,323,647 and 4,190,496, the disclosures of which are incorporated herein.

For diagnostic use, the antibodies may typically be distributed in multicontainer kit form. These kits will typically contain the antibody(ies) in labeled or unlabeled form in suitable containers, any detectable ligand reactive with unlabeled antibody if it is used, reagents for the incubations and washings if necessary, reagents for detecting the label moiety to be detected, such as substrates or derivatizing agents depending on the nature of the label, product inserts and instructions, and a positive control associated with LQT syndrome, SQT syndrome, Brugada syndrome and progressive conduction disease. The antibodies in the kit may be affinity purified if they are polyclonal.

The following examples are included for purposes of illustrating certain aspects of the invention. Accordingly, the examples should not be construed as limiting the subject matter of the present invention.

EXAMPLE I KCNH2 Mutations

1. Clinical Evaluation

Family 30-371 (FIG. 1), having 23 members, displayed a high incidence of sudden death. The proband (III-2) was referred due to frequent palpitations. Her ECG displayed a QT interval of 270 msec. Her daughter (IV-5) had a QT interval of 260 msec, but was asymptomatic. The proband's nephew (V-3) had a history of syncope and had a QT interval of 240 msec. The proband's sister (III-1), who had a QT of 210 msec and suffered from atrial fibrillation, died suddenly at age 62; her mother (II-3) died suddenly at age 45 and her nephew died suddenly with documented ventricular fibrillation at age 26 (IV-1). Eight living family members underwent a complete physical examination and a 12-lead ECG as part of their initial clinical work-up. Three presented with a short QT interval and were evaluated with additional tests, including MRI. Two of the affected individuals underwent an electrophysiological study.

Family 30-335, having 16 individuals, included three patients referred for palpitations, syncope and sudden death in one They also underwent extensive work-up including MRI and two underwent electrophysiological study. Three of the 16 members were affected with short QT syndrome. The proband (IV-2) was referred for history of syncope during exertion and paroxysmal atrial fibrillation. His QT interval ranged from 240 msec to 280 msec. His sister (IV-1) had a long history of palpitations and a QT interval between 220 and 250 msec. Her son (V-1), 6 years old, had suffered aborted sudden death at age 8 months, and had severe neurological damage. His ECG showed a QT interval ranging from 240 to 260 msec. Family history was significant for the death of the probands' brother (IV-3), when he was 3 months old, and their father who died suddenly at age 39 (III-2). Autopsy showed a normal heart in both. There were three other members who died suddenly.

2. Genetic Analysis

Genomic DNA was isolated from peripheral blood leukocytes using a commercial kit (Gentra System, Puregene). Haplotype segregation analysis was performed in family 30-371 by amplification of highly polymorphic markers (Linkage mapping set 2.5 Applied Biosystems) flanking the candidate genes with the use of polymerase chain reaction (PCR). Those genes that were segregating with the affected individuals were further analyzed.

The exons of KCNH2 were amplified and analyzed by direct sequencing using the primers set forth below. PCR products were purified with a commercial reagent (ExoSAP-IT™, USB) and were directly sequenced from both directions with the use of ABI PRISM 3100-Avant™ Automatic DNA Sequencer.

Seq. PRIMERS FOR Id. KCNH2 SCREENING No. KCNH2 EXON 1 GGCAGACAGGTGTGCCGG 103 SENSE KCNH2 EXON 1 CCATCCACACTCGGAAGAG 104 ANTISENSE KCNH2 EXON 2 CTGTGTGAGTGGAGAATGTG 105 SENSE KCNH2 EXON 2 GTGGTCCCGCCCCTCTTGAC 106 ANTISENSE KCNH2 EXON 3 CTTGGGTTCCAGGGTCCATC 107 SENSE KCNH2 EXON 3 GACCTTGGACAGCTCACAG 108 ANTISENSE KCNH2 EXON 4 GTCCATTTCCCAGGCCTTG 109 SENSE KCNH2 EXON 4 GACGTAGTGAAAAGGTCAGAAG 110 ANTISENSE KCNH2 EXON 5 GTCTCCACTCTCGATCTATG 111 SENSE KCNH2 EXON 5 CCCGGCTCTGGATCACAG 112 ANTISENSE KCNH2 EXON 6 CAGAGATGTCATCGCTCCTG 113 SENSE KCNH2 EXON 6 CACTACCTCCCACCACATTC 114 ANTISENSE KCNH2 EXON 7 CTTGCCCCATCAACGGAATG 115 SENSE KCNH2 EXON 7 CTAGCAGCCTCAGTTTCCTC 116 ANTISENSE KCNH2 EXON 8 CTGAGACTGAGACACTGAC 117 SENSE KCNH2 EXON 8 GTCCTTACTACTGACTGTGAC 118 ANTISENSE KCNH2 EXON 9 CTGGAGGTTGAGATTTCTCTG 119 SENSE KCNH2 EXON 9 GAAGGCTCGCACCTCTTGAG 120 ANTISENSE KCNH2 EXON 10 GTGCCTGCTGCCTGGATG 121 SENSE KCNH2 EXON 10 CATTCAATGTCACACAGCAAAG 122 ANTISENSE KCNH2 EXON 11 CTGTGTTAAGGAGGGAGCTTG 123 SENSE KCNH2 EXON 11 GCCTGGGTAAAGCAGACAC 124 ANTISENSE KCNH2 EXON 12 CTCCTCTCTGTTCTCCTCC 125 SENSE KCNH2 EXON 12 CAGAGAGCAGAGCTGGGTG 126 ANTISENSE KCNH2 EXON 13 CTGTCAGGTATCCCGGGC 127 SENSE KCNH2 EXON 13 CAGGACCTGGACCAGACTC 128 ANTISENSE KCNH2 EXON 14 GTGGAGGCTGTCACTGGTG 129 SENSE KCNH2 EXON 14 GAAAGGCAGCAAAGCAGGTTTG 130 ANTISENSE KCNH2 EXON 15 GTTCTCCTGCCCCTTTCCC 131 A SENSE KCNH2 EXON 15 CTTTCGAGTTCCTCTCCCC 132 A ANTISENSE KCNH2 EXON 15 CAGTGTGGACACGTGGCTC 133 B SENSE KCNH2 EXON 15 CTATGCATGTCCAGACAGGAAC 134 B ANTISENSE 3. Site-directed Mutagenesis

C1764A mutation was constructed with the use of GeneTailor™ site-directed mutagenesis system (Invitrogen Corp) with the use of plasmid pcDNA3.1 containing KCNH2 cDNA. The primers for were the following:

1764F (5′-GACTCACGCATCGGCTGGCTGCACAAACTG (Seq. Id. No. 7) GGCGACCAG-3′) and 1764R (5′-GTGCAGCCAGCCGATGCGTGAGTCCATGTG (Seq. Id. No. 8) T-3′).

The mutated plasmid was sequenced to ensure the presence of the C1764A mutation, as well as the absence of other substitutions introduced by the DNA polymerase.

4. In-vitro Transcription and Mammalian Cell Transfection

KCNH2 and KCNE2 were a kind gift from Drs. A. M Brown (Chantest, Cleveland, Ohio) and S. A. Goldstein (Yale University, New Haven, Conn.), respectively. Both gene constructs were re-cloned from their original vector into pcDNA3.1 (Invitrogen, Carlsbad, Calif.). For transfection, KCNH2 and KCNE2 cDNA were kept at a constant molar ratio of 1:20 to ensure proper expression of both subunits. Modified human embryonic kidney cells (TSA201) were co-transected with the same amounts of pcDNA-KCNH2/KCNE2 and pcDNA-N588K.KCNE2 complex using the calcium phosphate precipitation method. Cells were grown on polylysine coated 35 mm culture dishes and placed in a temperature-controlled chamber for electrophysiological study (Medical Systems, Greenvale N.Y.) 2 days post-transfection.

5. Electrophysiology

Standard whole cell patch clamp technique was used to measure currents in transfected TSA201 cells. All recordings were made at room temperature using an Axopatch 1D amplifier equipped with a CV-4 1/100 headstage (Axon Instruments). Cells were superfused with HEPES-buffered solution containing (in mmol/L): 130 NaCl, 5 KCl, 1.8 CaCl₂, 1. MgCl₂, 2.8 Na acetate, 10 Hepes, pH 7.3 with NaOH/HCl. Patch pipettes were pulled from borosilicate (7740) or flint glass (1161) (PP89 Narahige Japan) to have resistances between 2 and 4 MΩ when filled with a solution containing (in mmol/L): 20 KCl, 120 KF, 1.0 MgCl₂, 10 HEPES and EGTA, pH 7.2 (KOH/HCl). Currents were filtered with a four pole Bessel filter at 0.5 to 1 kHz, digitized at 1 kHz and stored on the hard disk of an IBM compatible computer. All data acquisition and analysis was performed using the suite of pCLAMP programs V7 or V6 (Axon Instruments, CA).

EXAMPLE II SCN5A and KCNQ1 Mutations

1. Genetic Analysis

Genomic DNA was isolated from peripheral blood leukocytes using a commercial kit (Gentra System, Puregene). Haplotype segregation analysis was performed in family 30-371 by amplification of highly polymorphic markers (Linkage mapping set 2.5 Applied Biosystems) flanking the candidate genes with the use of polymerase chain reaction (PCR). Those genes that were segregating with the affected individuals were further analyzed.

The exons of SCN5A and KCNQ1 were amplified and analyzed by direct sequencing using the primers set forth below. PCR products were purified with a commercial reagent (ExoSAP-IT™, USB) and were directly sequenced from both directions with the use of ABI PRISM 3100-Avant™ Automatic DNA Sequencer.

Seq. Id. No. PRIMERS FOR SCN5A SCREENING SCN5A EXON 2 GGTCTGCCCACCCTGCTCTCT 9 SENSE SCN5A EXON 2 CCTCTTCCCCCTCTGCTCCATT 10 ANTISENSE SCN5A EXON 3 AGTCCAAGGGCTCTGAGCCAA 11 SENSE SCN5A EXON 3 GGTACTCAGCAGGTATTAACTGCAA 12 ANTISENSE SCN5A EXON 4 GGTAGCACTGTCCTGGCAGTGAT 13 SENSE SCN5A EXON 4 CCTGGACTCAAGTCCCCTTC 14 ANTISENSE SCN5A EXON 5 TCACTCCACGTAAGGAACCTG 15 SENSE SCN5A EXON 5 ATGTGGACTGCAGGGAGGAAGC 16 ANTISENSE SCN5A EXON 6 CCTTTCCTCCTCTCACTGTCTGT 17 SENSE SCN5A EXON 6 GGTATTCTGGTGACAGGCACATTC 18 ANTISENSE SCN5A EXON 7 CCACCTCTGGTTGCCTACACTG 19 SENSE SCN5A EXON 7 GTCTGCGGTCTCACAAAGTCTTC 20 ANTISENSE SCN5A EXON 8 CGAGTGCCCCTCACCAGCATG 21 SENSE SCN5A EXON 8 GGAGACTCCCCTGGCAGGACAA 22 ANTISENSE SCN5A EXON 9 GGGAGACAAGTCCAGCCCAGCAA 23 SENSE SCN5A EXON 9 AGCCCACACTTGCTGTCCCTTG 24 ANTISENSE SCN5A EXON 10 ACTTGGAAATGCCCTCACCCAGA 25 SENSE SCN5A EXON 10 CACCTATAGGCACCATCAGTCAG 26 ANTISENSE SCN5A EXON 11 AAACGTCCGTTCCTCCACTCT 27 SENSE SCN5A EXON 11 AACCCACAGCTGGGATTACCATT 28 ANTISENSE SCN5A EXON 12A GCCAGTGGCTCAAAAGACAGGCT 29 SENSE SCN5A EXON 12A CCTGGGCACTGGTCCGGCGCA 30 ANTISENSE SCN5A EXON 12B CACCACACATCACTGCTGGTGC 31 SENSE SCN5A EXON 12B GGAACTGCTGATCAGTTTGGGAGA 32 ANTISENSE SCN5A EXON 13 CCCTTTTCCCCAGCTGACGCAAA 33 SENSE SCN5A EXON 13 GTCTAAAGCAGGCCAAGACAAATG 34 ANTISENSE SCN5A EXON 14 CAGGAAGGTATTCCAGTTACATATGA 35 SENSE SCN5A EXON 14 ACCCATGAAGCTGTGCCAGCTGT 36 ANTISENSE SCN5A EXON 15 CTTTCCTATCCCAAACAATACCT 37 SENSE SCN5A EXON 15 CCCCACCATCCCCCATGCAGT 38 ANTISENSE SCN5A EXON 16 GAGCCAGAGACCTTCACAAGGTCCCCT 39 SENSE SCN5A EXON 16 CCCTTGCCACTTACCACAAG 40 ANTISENSE SCN5A EXON 17A GGGACTGGATGGCTTGGCATGGT 41 SENSE SCN5A EXON 17A CGGGGAGTAGGGGGTGGCAATG 42 ANTISENSE SCN5A EXON 17B GCCCAGGGCCAGCTGCCCAGCT 43 SENSE SCN5A EXON 17B CTGTATATGTAGGTGCCTTATACATG 44 ANTISENSE SCN5A EXON 18 AGGGTCTAAACCCCCAGGGTCA 45 SENSE SCN5A EXON 18 CCCAGCTGGCTTCAGGGACAAA 46 ANTISENSE SCN5A EXON 19 GAGGCCAAAGGCTGCTACTCAG 47 SENSE SCN5A EXON 19 CCTGTCCCCTCTGGGTGGAACT 48 ANTISENSE SCN5A EXON 20 ACAGGCCCTGAGGTGGGCCTGA 49 SENSE SCN5A EXON 20 TGACCTGACTTTCCAGCTGGAGA 50 ANTISENSE SCN5A EXON 21 TCCAGGCTTCATGTCCACCTGTCT 51 SENSE SCN5A EXON 21 TCTCCCGCACCGGCAATGGGT 52 ANTISENSE SCN5A EXON 22 AGTGGGGAGCTGTTCCCATCCT 53 SENSE SCN5A EXON 22 GGACCGCCTCCCACTCC 54 ANTISENSE SCN5A EXON 23 TTGAAAAGGAAATGTGCTCTGGG 55 SENSE SCN5A EXON 23 AACATCATGGGTGATGGCCAT 56 ANTISENSE SCN5A EXON 24 CTCAAGCGAGGTACAGAATTAAATGA 57 SENSE SCN5A EXON 24 GGGCTTTCAGATGCAGACACTGAT 58 ANTISENSE SCN5A EXON 25 GCCTGTCTGATCTCCCTGTGTGA 59 SENSE SCN5A EXON 25 CCTGTCTGGTCTCCCTGTGTCA 60 ANTISENSE SCN5A EXON 26 CCATGCTGGGGCCTCTGAGAAC 61 SENSE SCN5A EXON 26 GGCTCTGATGGCTGGCCATGTG 62 ANTISENSE SCN5A EXON 27 CCCAGCGAGCACTTTCCATTTG 63 SENSE SCN5A EXON 27 GCTTCTCCGTCCAGCTGACTTGTA 64 ANTISENSE SCN5A EXON 28A TGCACAGTGATGCTGGCTGGAA 65 SENSE SCN5A EXON 28A GAAGAGGCACAGCATGCTGTTGG 66 ANTISENSE SCN5A EXON 28B AAGTGGGAGGCTGGCATCGAC 67 SENSE SCN5A EXON 28B GTCCCCACTCACCATGGGCAG 68 ANTISENSE SCN5A EXON 28C GTCCTGTCTGACTTTGCCGAC 69 SENSE SCN5A EXON 28C CATTTCTTACTCCCAAAGCCAG 70 ANTISENSE PRIMERS FOR KCNQ1 SCREENING KCNQ1 EXON 1 CTTGAGTGTGGAGGAGATAAGC 71 SENSE KCNQ1 EXON 1 CAAATTCCCGAGAGCCAGAAAC 72 ANTISENSE KCNQ1 EXON 2 CAGGTGCATCTGTGGGATG 73 SENSE KCNQ1 EXON 2 GGACCAATGTGTGGGCAAG 74 ANTISENSE KCNQ1 EXON 3 GTTCAAACAGGTTGCAGGGTC 75 SENSE KCNQ1 EXON 3 CTTAGGGGACTCCATCTGGTAG 76 ANTISENSE KCNQ1 EXON 4 GTGTATGCTCTTCCCTGGG 77 SENSE KCNQ1 EXON 4 GCATCTGAGCAAGGTGGATG 78 ANTISENSE KCNQ1 EXON 5 CGTGAACAGCTGAGCCCAG 79 SENSE KCNQ1 EXON 5 CATCTCAAGCTGTCCTAGTGTG 80 ANTISENSE KCNQ1 EXON 6 GACTCGCTGCCTTAGGCG 81 SENSE KCNQ1 EXON 6 GAAGTCTCAAGACACCAGTG 82 ANTISENSE KCNQ1 EXON 7 CATCAGAGTGGTGGGTTTG 83 SENSE KCNQ1 EXON 7 CTGAACGTAAGTGGGTCTG 84 ANTISENSE KCNQ1 EXON 8 CAACGGTGACCGGTAACCAC 85 SENSE KCNQ1 EXON 8 CTGGATGCAACAATAACAGTGAC 86 ANTISENSE KCNQ1 EXON 9 GAGCTGTAGCTTCCATAAGG 87 SENSE KCNQ1 EXON 9 CTGTACCAAGCCAAATGCATG 88 ANTISENSE KCNQ1 EXON 10 CTGTCCGGGTGTATGTGGC 89 SENSE KCNQ1 EXON 10 CAAAAAAGGCAGTGACCTTC 90 ANTISENSE KCNQ1 EXON 11 CACAGCACTGGCAGGTTG 91 SENSE KCNQ1 EXON 11 GGCCAGAGAGCAAGGCTTC 92 ANTISENSE KCNQ1 EXON 12 CAGTCTGCGTGCTCCTCAG 93 SENSE KCNQ1 EXON 12 CCTTGACACCCTCCACTATG 94 ANTISENSE KCNQ1 EXON 13 CAGGTCTTCACAAGCCTCC 95 SENSE KCNQ1 EXON 13 GTTGAGAGGCAAGAACTCAG 96 ANTISENSE KCNQ1 EXON 14 CAAGCTGTCTGTCCCACAG 97 SENSE KCNQ1 EXON 14 CTGGCTTTCATTTCATGTCATG 98 ANTISENSE KCNQ1 EXON 15 GTAGGTTTAGGCATTTTGACTC 99 SENSE KCNQ1 EXON 15 CTTCACGTTCACACGCAGAC 100 ANTISENSE KCNQ1 EXON 16 CTGAGGCTGTCTGCACAC 101 SENSE KCNQ1 EXON 16 GTGGCCTCCTTCAGAGAG 102 ANTISENSE 2. In Vitro Transcription and Mammalian Cell Transfection Gene constructs were re-cloned from their original vector into pcDNA3.1 (Invitrogen Carlsbad, Calif.). F532C mutation was constructed with the GeneTailor™ site-directed mutagenesis system (Invitrogen Corp) on plasmid pcDNA3.1 containing the appropriate primers. The mutated plasmid was sequenced to ensure the presence of mutation without spurious substitutions. Modified human embryonic kidney cells (TSA201) were co-transected with the same amounts of pcDNA using the calcium phosphate precipitation method. Cells were grown on polylysine coated 35 mm culture dishes and placed in a temperature-controlled chamber for electrophysiological study (Medical Systems, Greenvale N.Y.) 2 days post-transfection. 3. Electrophysiology

Voltage clamp recordings were made using patch pipettes fabricated from borosilicate glass capillaries (1.5 mm O.D., Fisher Scientific, Pittsburg, Pa.). The pipettes were pulled using a gravity puller (Narashige Corp.) and filled with pipette solution of the following composition (mM): 10 KCl, 105 CsF, 10 NaCl, 10 HEPES, 10 EGTA and 5 TEACl, pH=7.2 with CsOH. The pipette resistance ranged from 0.8-2.8 MO when filled with the internal solution. The perfusion solution contained (mM): 130 NaCl, 5 KCl, 1.8 CaCl₂, 1.0 MgCl₂, 2.8 Na acetate, 10 HEPES, 10 glucose, pH=7.3 with NaOH. Current signals were recorded using a MultiClamp 700A amplifier (Axon Instruments Inc., Foster City, Calif.) and series resistance errors were reduced by about 60-70% with electronic compensation. All signals were acquired at 20-50 kHz (Digidata 1322, Axon Instruments) and analyzed with a microcomputer running pClamp 9 software (Axon Instruments, Foster City, Calif.). All recordings were made at room temperature.

EXAMPLE III Correlation of Gene Mutation to Syndrome

Using the techniques described above, the following mutations were shown to correspond with the indicated clinical conditions:

Patient FAMILY Channel Exon Aminoacid position BRUGADA SYNDROME RB4901 24-310 SCN5A 28 C1727 R RB5145 24-345 SCN5A 3 R104W RB5037 24-328 SCN5A 16 insertionTG (851) RB4665 24-064 SCN5A 16 R878C RB5151 24-JPN3 SCN5A 12 F532C RB6011 24-365 SCN5A 16 L917R RB6130 33-433 SCN5A 6, 22 V232I + L1307F RB054 24-011 SCN5A 27splice28 deletion(E1573-G1604) RB5029 24-284 SCN5A 14 A735V RB6237 24-483 SCN5A 27 E1573K RB6026 24-372 SCN5A 5 R179 stop RB6179 25-440 SCN5A 10 E446K RB6181 25-442 SCN5A 10 G400A RB6267 24-492 SCN5A 16 H886P RB6042 24-347 SCN5A 9, 28 P336L, I1659V RB4060 24-096 SCN5A 28 Y1614 stop codon RB4510 SCN5A 6 T220I LONG QT SYNDROME RB6024 25-JPN1 KCNQ1 3 G189W RB6301 25-499 KCNH2 5 R356H RB6087 25-387 SCN5A 19 S1134I RB6188 25-449 KCNH2 9 C deletion (764) RB6194 25-454 KCNH2 6 W398stopcodon SHORT QT SYNDROME RB6019 30-371 KCNH2 7 N588K PROGRESSIVE CONDUCTION DISEASE RB6325 25-510 SCN5A 17 P1008S

It will be understood that various modifications may be made to the embodiments and examples disclosed herein. Therefore, the above description should not be construed as limiting, merely as exemplifications of preferred embodiments. Those skilled in the art may envision other modifications within the spirit and scope of the claims appended hereto. 

1. An isolated nucleic acid encoding a mutant KCNH2 protein having a modified amino acid sequence of the wild-type human KCNH2 protein (SEQ ID NO: 5), the mutant KCNH2 protein having at least one mutation selected from the group consisting of N588K, R356H , a C deletion at 764 and a W398 stop codon.
 2. An isolated nucleic acid according to claim 1 wherein the nucleic acid has a sequence corresponding to that of wild-type human KCNH2 cDNA (SEQ ID NO: 6) with a C to A substitution at nucleotide
 1764. 3. An isolated nucleic acid according to claim 1 wherein the nucleic acid has a sequence corresponding to that of wild-type human KCNH2 cDNA (SEQ ID NO: 6) with a C to G substitution at nucleotide
 1764. 4. An isolated vector comprising the isolated nucleic acid of claim
 1. 5. An isolated cell comprising the isolated nucleic acid of claim
 1. 